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410 Chapter 18 Free Energy and Thermodynamics 18.87 Given: + C₂H₄X₂(₈) where X = Cl, Br, and I Find: and K at 25 °C and spontaneity trends with X and temperature Conceptual Plan: = - then = - then °C K then J/K kJ/K then 1kJ K = 273.15 + °C AG then K Solution: Reactant/Product from Appendix IIB) 52.4 0.0 C₂H₄Cl₂(₈) -129.7 Be sure to pull data for the correct formula and phase. = = + = [1(-129.7kJ)] - [1(52.4kJ) + = [52.4kJ] = -182.1 kJ then Reactant/Product K from Appendix IIB) 219.3 223.1 C₂H₄Cl₂(₈) 308.0 Be sure to pull data for the correct formula and phase. = = + = [1(308.0J/K)] [1(219.3J/K) + 1(223.1 J/K)] = [308.0J/K] [442.4J/K] = -134.4J/K then T = 273.15 + 25 °C = 298 K then = then = = 182.1 = -142.0kJ = -1.420 X 10⁵ J then = K Rearrange to solve for K. K = = 7.78 X 10²⁴; so the reaction is spontaneous. Reactant/Product from Appendix IIB) C₂H₄(₈) 52.4 Br₂(g) 30.9 38.3 Be sure to pull data for the correct formula and phase. = = + = [1(52.4kJ) + = [38.3kJ] - [83.3kJ] = -45.0kJ then Copyright © 2017 Pearson Education, Inc.